Admin/makedist

--- a/Admin/makedist	Wed Jun 09 14:08:08 2010 +0200
+++ b/Admin/makedist	Wed Jun 09 15:09:00 2010 +0200
@@ -145,6 +145,11 @@
 rm -rf doc-src
 
 mkdir -p contrib
+cat >contrib/README <<EOF
+This directory contains add-on components that contribute to the main
+Isabelle distribution.  Separate licensing conditions apply, see each
+directory individually.
+EOF
 
 cp doc/isabelle*.eps lib/logo